A variety of techniques are currently available to physicians for controlling elongate medical devices such as catheters, endoscopes and other surgical tools within a patient. For example, magnetic steering techniques provide computer-assisted control of a catheter tip while allowing an operating physician to remain outside the operating room x-ray field. In such systems, there is often a lag between the direction of an applied magnetic field and the actual orientation of the distal end of the medical device that must be taken into account for navigation. Typically, the physician will advance the device only once the distal end of the medical device is in the desired orientation, which magnetic steering techniques may not always achieve by themselves: the applied torque might not be sufficient to overcome resistance, as for instance in areas of rapid blood flow; proximal device advancement might be ineffective due to device prolapse or buckling at a vessel branch. Further, magnetic navigation might not prevent dislodgment, for instance when a guide catheter has been inserted to a coronary ostium, and an interventional device is advanced past the guide catheter distal end; resistance to advancement might cause the guide catheter to become dislodged, and at the present time it is not possible to precisely control the magnetic field applied at the ostium when magnetically navigating the interventional device distal tip beyond the guide catheter distal tip. In endocardial applications using current magnetic navigation technologies, it might be difficult to maintain contact between an interventional device distal end and the moving heart wall, in particular upon oblique or glancing approaches where the distal end is not perpendicular to the tissue. U.S. Pat. No. 6,679,836 issued to Couvillon and assigned to SciMed Life Systems, Inc., describes a guide catheter apparatus comprising a plurality of electro-active polymer actuators disposed along its length, and methods of using the same; however that patent does not teach nor suggest the combinative use of electrostrictive materials with magnetic navigation. Similarly, published U.S. patent application No. 20050256398, filed by Hastings et al., describes methods and systems for interventional medicine, including the use of electrostriction to bend a medical device or selectively stiffen a medical device. Although that patent application does describe methods of magnetically navigating an interventional medical device, it does not teach nor suggest the combinative use of electrostriction with magnetic navigation. Combinative use of these approaches, as disclosed below, significantly improves upon the state-of-the-art and enables applications that could not have been successfully performed before.
Another motivation for the present invention is the possibility of improving the performance of a magnetic navigation system while reducing its size and cost. For example, reducing the size of the magnetic source magnets, made possible by electrostrictive torques applied at particular angles, could provide greater imaging and physician access. For example, the tip force required in certain ablation procedures in the heart, may be limited by the size of the source magnets, and can be improved by the addition of electrostriction.